Thin-film strain gauge

Abstract

A thin-film strain gauge and a method for producing it are proposed; the strain gauge is advantageously capable of integration into a thin-film circuit. The strain gauge comprises an elastically deformable spring element in combination with at least one elongation-sensitive resistor. The resistor disposition (R1-R4), the low-impedance connections (L11-L42) between the various resistance regions and the associated connection tracks (L5-L8) are applied in a vacuum process, preferably by cathode sputtering. The low-impedance connections (L11-L42) and the connection tracks (L5-L8) are of material which, although different from the material making up the actual resistance region, still has approximately the same temperature coefficient of resistance, so as to preclude errors caused by temperature.

We claim: 
     
       1. A temperature-compensated thin-film strain gauge, particularly a precision thin-film strain gauge capable of integration into a thin-film circuit, for measuring force, pressure, displacement, weight, or acceleration, having an elastically deformable spring device (10, S) in combination with at least one elongation-sensitive resistor element, having at least one deflectable resistance region (R1, R3) and one substantially non-deflecting resistance region (R2, R4);   at least one low-impedance connection element (L11-L42) connecting at least said resistance regions (R1, R3; R2, R4); and   connection tracks (L5-L8), wherein, to simplify production and facilitate integration of the gauge in a larger thin-film circuit, at least one of: the resistor element disposition (R1, R4);   the low-impedance connections (L11-L42) between the various resistance regions; and     associated connection tracks (L5-L8) are applied by means of at least one of thermal vapor deposition and cathode sputtering; and wherein, to prevent temperature fluctuations from giving rise to erroneous strain change measurements, the temperature coefficients of resistance (TCR's) of the materials used for the elongation-sensitive resistor element (R1-R4) and at least one of the low-impedance connections (L11-L42) and the connection tracks (L5-l8) are of the same order of magnitude; and wherein, to prevent loss of measurement signal strength, at least one of:   the low-impedance connections (L11-L42); and   the connection tracks (L5-L8) are of material which is different from the material of the resistance element regions (R1-R4).     
     
     
       2. Strain gauge according to claim 1, wherein the at least one elongation-sensitive resistor element comprises four elongation-sensitive resistors (R1, R4) combined into a Wheatstone bridge.   
     
     
       3. Strain gauge according to claim 1, wherein at least one of: the low-impedance connections (L11-L42);   the connection tracks (L5-L8) comprise constantan doped with nitrogen.   
     
     
       4. Strain gauge according to claim 3, wherein the at least one elongation-sensitive resistor element comprises four elongation-sensitive resistors (R1, R4) combined into a Wheatstone bridge.   
     
     
       5. Strain gauge according to claim 1, wherein the at least one elongation-sensitive resistor element (L1-L4) comprises tantalum nitride (Ta 2  N, TaN); or tantalum oxynitride (TaO x  N y ); or tantalum nitride and tantalum oxynitride.   
     
     
       6. Strain gauge according to claim 5, wherein the at least one elongation-sensitive resistor element comprises four elongation-sensitive resistors (R1, R4) combined into a Wheatsone bridge.   
     
     
       7. Strain gauge according to claim 1, wherein the spring device (10) is an elastically deformable device; a thin organic foil is adhesively connected to said spring device;   and the elongation sensitive resistor element (R1-R4) is applied on the thin organic foil.   
     
     
       8. Strain gauge according to claim 7, wherein the at least one elongation-sensitive resistor element comprises four elongation-sensitive resistors (R1, R4) combined into a Wheatstone bridge.   
     
     
       9. Strain gauge according to claim 1, further including an insulation layer (I) interposed between the spring device (10S) and the elongation-sensitive resistor element (R1, R4) vapor-deposited or sputtered on the insulation layer. 
     
     
       10. Strain gauge according to claim 9, wherein the at least one elongation-sensitive resistor element comprises four elongation-sensitive resistors (R1, R4) combined into a Wheatstone bridge.   
     
     
       11. Strain gauge according to claim 1, wherein said elongation-sensitive resistor elements (R1, R4) are connected in a Wheatstone bridge configuration, located in a rectangular disposition having two elongatable resistance regions (R1, R3) and two non-elongatable resistance regions (R2, R4), said resistance regions being applied onto the spring device (10); and wherein the spring device is deflectable at one end.   
     
     
       12. Strain gauge according to claim 11, wherein at least one of: the low-impedance connections (L11-L42);   the connection tracks (L5-L8) comprise constantan doped with nitrogen;   and wherein the at least one elongation-sensitive resistor element (L1-L4) comprises   tantalum nitride (Ta 2  N, TaN); or tantalum oxynitride (TaO x  N y ); or tantalum nitride and tantalum oxynitride.   
     
     
       13. Strain gauge according to claim 1, wherein said elongation-resistance resistance element (R1, R4) is connected in a Wheatstone bridge configuration having two resistance regions (R1, R3) shaped to be approximately semicircular, and being tangentially elongatable, and two resistance regions (R2, R4) which are radially elongatable, and approximately U-shaped; and the spring device comprises a round membrane on which said elongation-sensitive resistance element is applied.   
     
     
       14. Strain gauge according to claim 1, further including a poreless thin high-impedance glass insulation layer (I) being applied to the spring device (S); and wherein the elongation-sensitive resistance element (R1, R4) is applied over the glass insulation layer.   
     
     
       15. Strain gauge according to claim 14, wherein the spring device comprises a copper-beryllium (CuBe) spring plate.